A magnetic disk drive system is necessary for data processing in a computer, and is used to record, read and regenerate data as a hard disk drive (HDD) in a personal computer. Personal computers are becoming widespread. The application area of magnetic disk drive systems is recently becoming very wide and includes AV equipment, vehicle-mounted equipment, etc. in addition to personal computers. As the information handled by such equipment varies widely and the amount of the information might be enormous, the recording capacity of magnetic disk drive systems is being enlarged.
The conventional magnetic disk drive system used as a HDD roughly consists of two portions, a circuit board assembly portion and a disk enclosure portion, which are usually provided in a housing. The magnetic disk drive system is connected to a host system such as a personal computer.
The disk enclosure portion includes a magnetic disk which is rotated at a high speed in a certain direction, and a head which is movable in the radial direction intersecting the tracks on the disk, and the head is able to scan required tracks on the rotating disk. The recorded data read by the head is amplified and output as a regenerated signal. When a recording signal is supplied, data is sent to the head, the head is moved on the disk, and the data is recorded in a write position of a predetermined track.
In a magnetic disk drive system, data is written and recorded on the tracks, in a concentric circle form, on the disk traced by the head, and the recorded data is read and regenerated by the head tracing the tracks. The data is written by the write head Hw of the head and is read by the read head Hr of the head.
More than one servo data are disposed in a radial signal pattern on the disk, and highly accurate servo control of the disk is performed with these servo data, and high data density is realized. The servo data includes a servo mark, track data and sector data which are servo addresses, burst data, etc. The track data includes a track number, and the sector data includes a sector number showing the number of the sector on the track concerned. Usually, the track number is written with a gray code. The track number and sector number are detected with the head, and it is determined in which sector data is written or data from which sector is read.
The burst data included in the servo data is written following the gray code, and has information about the position of the head relative to the track. In general, the burst data consists of four signal patterns of the burst A to the burst D, and these four signal patterns are written on the four tracks respectively disposed in sequence in the radial direction. The relative position between the center of a track and the head can be calculated with the amplitude of the signal on the track read by the head.
By the way, the servo data is disposed so as to be in a plurality of sectors on the tracks in the radial positions on the disk. Consequently, the servo data is disposed at the head of each sector. Then, user data are distributed and written in the sectors. A predetermined amount of the user data is written in the portion following the position in which the burst D is written.
In case of a HDD used for a personal computer, the user data consists of a preamble, a sync mark, user data, an error-correcting code, and a postamble.
On the other hand, in many cases, a head assembly consisting of two heads, a write head and a read head, is used, and the two heads are disposed at the front end of the arm and at a distance from each other in the circumferential direction. Except for a head assembly having a single head by which data is written and read, there is a small difference between the write timing and the read timing because of the physical distance between the two heads.
Because of this, when the user data is written into a sector, it is required that the writing is started at the position at least at a distance between the write head and the read head or more from the burst D in order to prevent the data of the burst D from being overwritten. However, as the dimension of the distance between the installation positions of the write head and the read head is not strictly controlled, there is a variation of the distance between the head assemblies. Furthermore, the write timing fluctuates because it is designed based on the read time. For this reason, even if the write timing is delayed from the burst D by the distance between the write head and read head, there is a possibility of overwriting the data of the burst D.
In the conventional method of controlling the distance between two heads of a head assembly, the distance is not measured for every head assembly. Consequently, the write timing is so set that the writing of the user data is started at the position at a sufficient distance from the burst D in order to prevent the burst D being overwritten and erased under the influence of the variation of the distance between the write head and read head when the user data is written in a sector. Thus, there is a blank where no data exists between the burst D and the written user data. This is the main factor reducing the efficiency of the format of the disk and affects the efficient use of the disk.
It is therefore an object of the present invention to provide a magnetic disk drive system which improves the efficiency of the format of the disk by measuring the distance between heads for every magnetic disk drive system and adjusting the timing of writing data based on the result of the measurement.